1. Field of the Invention
This invention relates to driving circuits for switching devices such as IGBTs (Insulated Gate Bipolar Transistor) and semiconductor devices including the driving circuits.
2. Description of the Background Art
Conventional driving circuits for switching devices such as IGBTs generate pulse signals for turning the switching devices on and off based on edges of external input signals, and generate ON signals and OFF signals for controlling the switching devices based on those pulse signals level-shifted by level shift circuits. The driving circuits then supply the ON signals and OFF signals to the switching devices to bring them into a conducting state and non-conducting state, respectively, thereby switching the switching devices on and off. Other driving circuits for switching devices are disclosed in Japanese Patent Application Laid-Open Nos. 6-153533 (1994), 2003-101391 and 11-103570 (1999).
When the above conventional driving circuits are used to drive and cause a high-potential side switching device to transition from OFF to ON between two switching devices that are totem-pole-connected between a high potential and a low potential, the ON signals may not be generated depending on the transition timing. In short, the high-potential side switching device sometimes cannot be turned on despite the wish to do so. This problem will be described in detail.
When the high-potential side switching device makes an ON to OFF transition between the two totem-pole-connected switching devices as described above, a potential at a node between the two switching devices falls from a high level to become a negative potential. At this time, the node potential becomes less than a certain negative potential, whereby the output level of the level shift circuits is sometimes fixed at a low level, for example, for a certain period.
Accordingly, the pulse signals for the turning-on which may be generated based on the external input signals while the node potential is less than the certain negative potential are not accepted, making it impossible for the ON signals to be output. The result is that the high-potential side switching device cannot be turned on reliably based on the edges of the input signals.